Kaiserslautern - Fachbereich Chemie
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The direct regioselective C−H-functionalization of simple, unfunctionalized pyridines is considered a long-standing challenge in heterocyclic chemistry. Herein, we report a novel one-pot protocol for the C4-selective sulfonylation of pyridines via triflic anhydride (Tf2O) activation, base-mediated addition of a sulfinic acid salt, and subsequent elimination/re-aromatization. Contrary to previous approaches employing tailored blocking groups, positional selectivity can be controlled by using N-methylpiperidine as simple, readily available external base. This method offers a highly modular and streamlined access to C4-sulfonylated pyridines.
Janus-Materialien sind anisotrope Nano- und Mikroarchitekturen, die zwei verschiedene Seiten mit unterschiedlichen oder entgegengesetzten physikochemischen Eigenschaften aufweisen. Parallel zur Entwicklung neuer Methoden zur Herstellung dieser Materialien wurden entscheidende Fortschritte in Bezug auf Anwendungen erzielt, z. B. in der Biologie, der Katalyse, der Pharmazie und neuerdings auch in der Batterietechnologie. Dieser Kurzaufsatz stellt die jüngsten und wichtigsten Erfolge bei der Anwendung aufgabenspezifisch funktionalisierter Janus-Nanomaterialien im Bereich der heterogenen Katalyse für unterschiedliche chemische Transformationen vor. Er umfasst Reduktionreaktionen, oxidative Entschwefelung und Farbstoffabbau, asymmetrische Katalyse, Biomassetransformationen, Kaskadenreaktionen, Oxidationsreaktionen, übergangsmetallkatalysierte Kreuzkupplungsreaktionen, elektro- und photokatalytische Reaktionen sowie Gasphasenreaktionen. Zum Abschluss folgt ein Ausblick auf mögliche zukünftige Anwendungen.
A stereoselective synthesis of isoindolo[2,1-a]quinolin-11(5H)-ones containing three contiguous stereogenic centers is described. This Lewis-acid mediated reaction of enamides with N-aryl-acylimines affords the desired fused heterocyclic isoindolinones in high yields and diastereoselectivities. Scope and limitations of this method are discussed. The stereochemical outcome of this transformation indicates a stepwise reaction pathway.
A novel method for the synthesis of nitro fatty acids (NFAs), an intriguing class of endogenously occurring lipid mediators, is reported. This one-pot procedure enables the controlled and stereoselective construction of nitro fatty acids from a simple set of common building blocks in a highly facile manner. Thereby, this methodology offers a streamlined, highly modular access to naturally occurring nitro fatty acids as well as non-natural NFA derivatives.
Sulfones play a pivotal role in modern organic chemistry. They are highly versatile building blocks and find various applications as drugs, agrochemicals, or functional materials. Therefore, sustainable access to this class of molecules is of great interest. Herein, the goal was to provide a summary on recent developments in the field of sustainable sulfone synthesis. Advances and existing limitations in traditional approaches towards sulfones were reviewed on selected examples. Furthermore, novel emerging technologies for a more sustainable sulfone synthesis and future directions were discussed.
A concept for the quantification of cooperative effects in transition-metal complexes is presented. It is demonstrated for a series of novel N,N- (mononuclear) and C,N-coordinated homo- and heterometallic binuclear complexes based on the (2-dimethylamino)-4-(2-pyrimidinyl)pyrimidine ligand, which are accessible by applying roll-over cyclometallation. These iridium-, platinum-, and palladium-containing compounds are investigated with respect to their absorption and fluorescence spectra. The cooperative effects in the electronic absorptions, i. e., the energetic shifts between mononuclear and dinuclear complexes, and free ligands are analyzed on the basis of the lowest energy π-π* transitions and compared to calculated data, obtained from TD-DFT calculations. Furthermore the corresponding fluorescence spectra are presented and analyzed with respect to the concept of cooperativity.
A highly diastereoselective one-pot synthesis of the 1,3-diamino-2-alcohol unit bearing three continuous stereocenters is described. This method utilizes 2-oxyenamides as a novel type of building block for the rapid assembly of the 1,3-diamine scaffold containing an additional stereogenic oxygen functionality at the C2 position. A stereoselective preparation of the required (Z)-oxyenamides is reported as well.
Palladium-Catalyzed Decarboxylative 1,2-Addition of Carboxylic Acids to Glyoxylic Acid Esters
(2021)
The formation of C−C-bonds constitutes one of the most fundamental synthetic operations in organic chemistry. The nucleophilic addition of preformed organometallic reagents to an electrophilic carbonyl functionality represents a classical method for the selective construction of a C−C-bond. However, the synthesis and utilization of an organometallic reagent is associated with an unfavorable environmental profile. Herein, we disclose a Palladium-catalyzed decarboxylative 1,2-addition of carboxylic acids to glyoxylic acid esters. This novel method provides access to the mandelic acid scaffold in good yields. Easy-to-handle and readily available benzoic acids are utilized as more sustainable alternative to preformed organometallic nucleophiles.
Es wird eine hochgradig diastereoselektive Eintopf-Synthese der 1,3-Diamino-2-Alkohol-Einheit mit drei fortlaufenden Stereozentren beschrieben. Bei dieser Methode werden 2-Oxyenamide als neue Bausteine für den raschen Aufbau des 1,3-Diamin-Gerüsts, mit einer zusätzlichen stereogenen Sauerstofffunktionalität in C2-Position, eingesetzt. Zusätzlich wird über eine stereoselektive Synthese der erforderlichen (Z)-Oxyenamide berichtet.
Using the mixed-metal approach, a direct synthesis route at ambient pressure was developed for a new type of bimetallic metal-organic framework based on the CPO-27 structure. The structural characterization of CPO-27(Cu0.6−CS−Co0.4) using X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray mapping and X-ray absorption spectroscopy revealed that the Cu2+ and Co2+ ions were exclusively incorporated at the metal positions of the CPO-27 lattice, but with a core-shell distribution within the crystallites. The parent framework material was then utilized as a precursor for the generation of novel bimetallic carbon-supported materials using the controlled thermal decomposition in a reducing atmosphere. During this decomposition process, the distribution of the two metals remained the same, which resulted in unique needle-shaped particles with a high dispersion of cobalt at the periphery of the amorphous carbon and agglomerated copper particles in the inside.